Error code F5

We sincerely apologise for the inconvenience caused.
Please reset the device and then charge it using a standard household socket for at least 30 minutes before checking whether normal operation has been restored.
To reset the device, press and hold both the DISPLAY and USB buttons simultaneously for 10 seconds. The display will briefly show “8888”, after which it will return to the normal screen — this indicates that the reset has been completed successfully.